I had unprotected sex with my SO on the 10th and 11th of September (after my fertile window). I started my period on 13 September and I am pretty much on my last day today (just light brown spotting here and there). My period was lighter this cycle. Also, my breasts are extremely sore (just started today) and this is unusual for me at the end of my period. My question is...with having unprotected sex so close to the start date of period and I started on time, is there a chance I could still be pregnant?